Isocyanurate ring-containing materials are usually prepared by trimerizing an organic isocyanate compound in the presence of a catalyst. Catalysts suitable for the trimerization include organic strong bases such as alkali metal salts of carboxylic acids, alkali metal phenolates, alkali metal carbonates, tertiary amines, tertiary phosphines, onium compounds of nitrogen or phosphorus, and as well as heterocyclic compounds containing such elements [see J. H. Saunders and K. C. Frisch, "Polyurethanes: Chemistry and Technology" (1962), p. 94]. Moreover, it is known that the reaction products of Mannich bases or tertiary amines with alkyl esters of phosphoric acid, phosphorous acid or phosphoric acid can also be used as trimerization catalysts.
However, such conventional trimerization catalysts have the disadvantage that they tend to yield yellow-colored reaction products. Another disadvantage thereof is that, where 2,4-tolylene diisocyanate is used as the starting material, it is very difficult to yield its trimer selectively without careful control of reaction conditions such as the amount of catalyst, reaction temperature and reaction time. Consequently, polynuclear by-products having poor solubility tend to be formed.
The object of the present invention is to overcome the above described disadvantages of the prior art processes for preparing the trimers of organic isocyanate compounds by using conventional catalysts.
As a result of extensive investigation of the reactions of isocyanates, the present inventor has found that potassium fluoride catalytically accelerates the trimerization of organic isocyanate compounds. The present invention has been completed on the basis of this finding.